Brake problem

[ccgeezer]

Hello,

 

My '97 Pathfinder, has new Big O Big Foot tires and was given a check up at the Carmax shop where I bought it and my own mechanic looked at it this morning to no avail.

 

Here's the problem: Traveling on the freeway doing 65 when I had to brake hard to avoid hitting a braking car in front of me. The feeling was that the front of the truck was dipping to the right and the rear of the truck was swerving hard to the left. Unnerving to say the least. I plan to try to duplicate the situation tomorrow but I feel that braking even at slower speeds tends to make the vehicle act the same.

 

My mechanic checked the pads and rotors but didn't find anything abnormal. There is a valve of some sort under the rear of the truck that is attached to the body and the brake line runs through it. He doesn't know what this is and suspects that it might be contributing to the problem. I think that it has something to do with the amount of load in the truck somehow related to the rear brake pressure. Anyway...

 

I sure would like some advice because my 30 day everything Carmax warranty expires on the 17th.

 

Thanks,

 

ccgeezer

[lewisnc100]

The valve you are talking about is the Load Sensing Valve and it does regulate the pressure sent to the brakes. Pretty difficult to test the brake pressures but you can test the spring length to make sure it is adjusted correctly. Without weight (person in front seat and rear, person in rear gets out slowly, gradually depress brake pedal) the spring length on the LSV should be 194mm (7.64 inches). With weight (place weight over the rear axle) the spring length should be 235mm (9.25 inches).

 

There was a quality control campaign that included your 97 and checked the LSV adjustment, rear diff, tires, struts, power steering switch etc. The number on this was 97-043 - Campaign - Quality Control Policy. You might call Nissan and check if that was ever done on your Pathfinder and if not check if it can be done.

 

Also you might read some of the past posts on the symptoms when the rear end bushings go bad, pretty common on your 97.

[Mookie]

Do you get swaying at highway speeds when you are not braking? Could be the rear link bushings are gone.

[ccgeezer]

Thanks for the info. I'll call the local Nissan dealer tomorrow about that quality control campaign. When I'm driving normally there isn't any sway, so I hope I can discount the rear link bushings.

[Mr. Pickles]

The feeling was that the front of the truck was dipping to the right and the rear of the truck was swerving hard to the left.

Couldn't this also be an issue of one side of the front brakes grabbing harder than the other, which would cause the truck to pull when braking?

[herm]

I'd suspect the brakes are fine and the suspension is worn out just enuf to not be able to handle the increase loads of heavy braking. Front struts may be going, maybe one side is softer than other, and as mentioned before look at the upper and lower control links. It's not uncommon to have to replace the 4 links and struts around 70,000 miles.

 

Check to see if the bumpstops are in the rear coils - they attach inverted within the coils - when they break off that is a sign the coils are soft.

 

But the control links and struts play a big role in what you feel at the 4 corners of the vehicle.

 

Look for leaks in the struts, and wear or cracks in the rubber bushings of the control links.

 

mike